February, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
a normal paraffin hydrocarbon was used in the synthetic mixture, the explanation may lie in the possibility that the paraffin hydrocarbons in the natural, cracked fuel are of branched-chain structure. Similar considerations apply in a less degree to the cracked Pennsylvanian and the straightrun midcontinent fuels. This point may serve also to explain the case of gasolines 8, 9, and 17, containing by analysis an appreciable aromatic equivalent, but actually requiring, by engine test, from 3 to 19 per cent of kerosene mixed with the standard for balance. Conclusions
a result of chemical analyses and engine tests on eighteen gasolines, it would appear that the method of evaluation of motor fuels here considered has given results agreeing approximately with engine tests for about half of the fuels studied. The other gasolines examined showed rather wide discrepancies between the findings of analysis and engine test. It is not believed that the antiknock value of gasolines can be satisfactorily determined by this method. 1-AE
231
2-Vsing pure hydrocarbons, an equivalence in knock reduction of approximately 2 : 2 : 1 has been found for a naphthene, an olefin, and an aromatic hydrocarbon, as represented by methylcyclohexane, hexylene, and toluene. 3-Qualitative evidence has been found for the idea that there are striking differences in the detonating tendency of the paraffin hydrocarbons present in different gasolines. Normal heptane was found to knock harder than petroleum paraffins and this may indicate the desirability of branched-chain paraffins as motor fuels. 4-The authors do not know of any dependable method for determining the detonating tendency of motor fuels except that of direct engine tests. Acknowledgment
The authors wish to acknowledge their indebtedness to
W. A. Gruse, of Mellon Institute, for valuable suggestions, and to J. 0. Timms, W. H. Ragsdale, and E. C. Martin, who aided in the experimental part of these investigations.
Influence of an Antiknock Compound in a Gas-Ion Oxidation’ By S. C. Lindz and D. C. Bardwell FIXEDNITROGEN RESEARCH LABORATORY, BURSAW
OF SOILS, WASHZNGTON,
D.c.
The actual comparison of the rates, with and without diethyl selenium, of the slow oxidation of methane under the ionizing influence of alpha-radiation does not indicate any retardation by ihe antiknock compound but rather some acceleration. The interpretation of this and its possible bearing on antiknock theory are discussed. UMEROUS efforts have been made to find a satis- was selected as the antiknock compound, instead of lead tetrafactory theory for the action of the antiknock com- ethyl. pounds of M i d g l e ~ . ~In 1924 Wendt and Grimm4 Experimental Method made experiments which they believed would support an electronic theory of detonation and at the same time explain The method employed was essentially that which the writers its suppression by antiknock compounds. Their experiments have used in measuring the velocity of various reactions.’ consisted in passing air that had been ionized by passage It consisted in saturating a mixture of C& 202 with through an arc, over a pool of benzene with or without dis- selenium diethyl a t 22.4’ C., where the vapor pressure of the solved tetraethyl lead or aniline. They found that a smaller latter is 38.4 mm., and then diluting samples of the saturated proportion of ions reached an electroscope placed in the air gas to give mixtures 0.001, 0.01, and 0.046 (almost saturated stream beyond the benzene pool when the latter contained a t 25” C.) molars with respect to selenium diethyl. These an antiknock than when it did not. From this they con- mixtures were introduced into the glass reaction spheres of cluded that the function of the antiknock is to cause the about 2 cm. diameter to which suitable amounts of radon more rapid recombination of gas ions, and if we admit the had been added. The course of the reaction was followed latter to be a positive factor in detonation, its suppression by means of the decrease of pressure (see tables). would result. Experimental Results More recently, however, Clark, Brugmann, and Thees have used x-radiation as a more constant source of ionization Preliminary tests showed that the oxidation of methane in and fail to find that the presence of an antiknock influences the absence of L‘antiknock’l could be readily measured the rate of recombination of the ions. manometrically.9 The opportunity for a more direct test seems to be offered The oxidation proceeds, apparently in one step, completely by studying the influence of an antiknock on a slow oxidation to form water and carbon dioxide: known to be proceeding under ionizing influence. The CHI 202 = Cot 2Hz0 slow oxidation of methane a t ordinary temperature under Chemical determination of carbon dioxide affords a final check the ionizing influence of radon was chosen as a suitable reon the reaction assumed. action. On account of its greater volatility, selenium diethyl6
N
+
+
1 Presented under the title “Etlects of Antiknock in Slow Oxidation of Methane under Influence of Ionization” before the Division of Gas and Fuel Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 t o 11, 1926. 2 Present address, University of Minnesota, Minneapolis, Minn. I THISJOURNAL, 16, 421 (19’23) I b i d . , 16, 890 (1924). 6 I b i d . , 17, 1226 (1926). 6 Mr. Midgley was kind enough t o furnish a supply of selenium diethyl.
+
Calculations
The kinetics have been calculated by use of the general equation : 7 J. Am. Chem. Soc., 41, 531, 551 (1919); 46, 2003 (1924); 47, 2675 (1925); 48, 1556, 1575 (1926). 8 “Molar” in this paper means the mol fraction. 0 Lind and Bardwell, J . A m . Chcm. Soc., 4S, 2335 (1926).
INDUSTRIAL A N D ENGINEERING CHEiVISTRY
232 -dP =
dt
Tables I, 11, and I11 give the results obtained with three concentrations of selenium diethyl beginning with the lowest 0.001 molar, which approximates the concentration used in actual automotive practice.
kpE,.P
which shows that the rate of pressure change is proportional to two variables, the pressure, P, and the amount of emanation, Et, present a t any time, t, and to the two constants, k, the ionization constant, and g, an efficiency factor for the conversion of ionization into chemical action. The integrated form of the equation for stepwise calculation is: Velocity constant = kP - = Eo(e-XtI log PdP2 - e-xt,,
T a b l e 111-Slow
"IME
h
D a w Hours
The constant k p , A is the combined constant from k , p , a n d X (the decay constant for radon) and has been evaluated to the following definition: for any given volume kp/X expresses the number of times that that volume of the reactants could be "cleaned up" by the complete decay of 1 curie of radon if the reactants were replenished to maintain any given constant pressure. Therefore kp/X is dependent on the volume, varyipg inversely with the square of the diameter of the reaction sphere; but M / N calculated from it is an independent constant characteristic of the reaction and expresses the number of any specified molecules reacting per ion pair, N . T a b l e I-Slow
:"-"x9" Days 0
0 3.0 6.25 9.0 17.5 20.0 22.5 5.33 19.5 19.5 19.5
Hours % 100.000 0
94.885 7 87.701 17.5 1 . 2 5 82.748 1 8 . 0 72.979 2 . 6 7 68.376 60.957 18.0 42.528 18.0 29.452 19.0 14.414 18.0 0.000 Final analysis
Total CH4+20r COz (-"20 v.) (calcd.) (calcd.
Mm. 706.0 598.1 500.9 443.5 364.9 338.3 306.6 262.5 260.7 259.9 241.5 242.0{ ~
Mm.
(?)'
- M ( a ~ a+ 02) N ( ~ ~
Mm. 5.0 4.2 4.6 4.7 4.8 4.8 5.1
Oxidation of M e t h a n e b y A1 h a - R a d i a t i o n in the Presence of 0.046 M Se(C&P
y:? To 100.000 97.775 95.421 93.473 87.700 86.071 84.473 80.253 72.163 60.277 50.333 I _
PRESSURE Total CH4+20z C02 ( - H z 0 v.). (calcd.) . . (calcd.1 .
Mm. 498.2 415.0 383.6 359.6 309.6 298.9 288.2 263.1 228.7 220 I2 219.8
Mm. 470.1 345.3 298.2 262.2 187.2 171.1 155.1 117.4 65.8 53.1 52.4
.
(?)'
-M(CH4+02)
N
(
~
~
~
Mm. ~~
0
41.6 57.3 69.3 94.3 99.6 105.0 117.5 134.7 139.0 139.3
(97.8) (11.0) 41.7 4.7 46.4 5.2 40.8 4.6 38.6 4.3 43.0 4.8 45.8 5.0 49.5 5.4 (14.6) (1.6) (1.1) Wtd. av. 4 . 7
a Reaction sphere: yolume 3.959 cc diameter 1.963 cm: temperature, 25' C.; Eo = 0.1416 curie. RLaction mixture: CH, 20r'(+28.1 mm. Se(CnHs)d.
+
Discussion
O x i d a t i o n of M e t h a n e b y AI h a - R a d i a t i o n in t h e P r e s e n c e of 0.001 M Se(Cz&za PRESSURE
Vol. 19, No. 2
The experimental results shown in the foregoing tables are summarized in Table IV. ~
+ ~ ~ ) T a b l e IV-Summarized Data 0 0.001 Molar fraction of Se (CzHdz in gas mixture Number of molecules of methane and oxygen reacting per ion pair 4.3 4.7
0.01
0.046
6.2
4 7
It will be seen that selenium diethyl exerted no retarding
influence on the rate of the reaction. In all cases the M / N ratio is greater in the presence of "antiknock" than in its absence. We have no explanation for the maximum rate exhibited by the 0.01 molar mixture. But even 6.2 hardly 10 exceeds the theoretical 6.0 to be expected from the general ~ 225,0 1 Wtd. ~ av. 4:. 7 ~ empirical rule for reactions of oxidation already stated. The velocity constants calculated stepwise agree about a Reaction sphere: volume, 4.315 cc.; diameter, 2.013 cm.; temperaas well as is usual in this kind of work. Toward the end of ture, 25O C.; E1 = 0.1232 curie. Reaction mixture: CHI + 202. the reaction the variations become greater and some deviation By analogy from other oxidations, such as those of hydrogen of final analysis as predicted from the total pressure drop and of carbon monoxide, we should expect for methane oxida- and the reaction equation is observed, which may be attributed tion to two factors-the possible interactions of Se(C2H5)2 itself, 2(CH4 202) = 2CO2 4-4Hz0 especially a t the highest concentration (0.046 M ) ; and to the per ion pair, or six molecules of methane and oxygen reacting for each pair of ions produced in the mixture. The value interaction of carbon dioxide, which is found by analysis to be deficient a t the end of the reaction. Oxygen was six was not attained in the normal mixture containing no antiknock, but is more nearly approached in its presence, added equivalent to methane, but not to selenium diethyl. This would leave an excess of combustible gas, either methane and is attained or even slightly exceeded in the 0.01 molar or selenium diethyl, as indicated by the final presence of mixture (Table 11). free hydrogen and the deficiency of carbon dioxide. T a b l e 11-Slow O x i d a t i o n of M e t h a n e b y A l p h a - R a d i a t i o n in t h e The fate of selenium diethyl itself was not determined, P r e s e n c e of 0.01 M Se(CzH5)a" but the indirect evidence, as well as analogy with other PRESSURE - M ( C H+~ 0 2 ) hydrocarbon reactions, leads to the belief that it reacts R,"_"h9" ( - Total CHI + 202 Cor N ( ~ oz) ~ ~ (probably + is oxidized) simultaneously with the methane. Hz0 v.) (calcd.) (calcd.) It requires 7.5 times its own volume ol oxygen for complete Mm. Mm. Mm. oxidation to water, carbon dioxide, and selenium dioxide. 0 32.0 At 0.001 molar concentration its quantity is too small to 45.5 99.1 affect the manometric results appreciably. But a t 0.01 114.1 molar it would require about 50 mm. of oxygen for its com133.2 151.4 plete oxidation. On account of its high molecular weight 172.6 183.6 and consequent high stopping power for alpha particles, a 193.5 considerable proportion of the total ionization will be pro201.1 206.4 duced on it. Consequently, it may react somewhat pref211.7 215.0 erentially compared with methane, and since it would have 218.4 ~~ a high -M / N ratio [theoretically fM(BeEh + o ~ ) / N ( s+ ~0,)E = 221.6 225.7 17)it would tend to raise the total - M / N ratio for the entire 236.6 173.3b reaction. Quite probably the higher values found are to be Analysis Wtd. av. 6 . 2 explained on this ground rather than on any specific catalytic a Reaction sphere: volume 4.555 cc.; diameter 2.057 cm.; temperature, effect. Decrease of - M / N on passing from 0.01 to 0.046 25' C.;E1 = 0.0965 curie. Reaction mixture: CH4 + 2 0 2 . b These disagreements between final analysis and manometry are molar mixture is probably to be explained by some reaction probably due to removal of carbon dioxide by secondary reaction with which Se(C2H& itself may undergo, producing an increase methane and with hydrogen.9 1
2 2 4 6
~~
+
(?)'
+
~
INDUSTRIAL S X D E S G I S E E R I S G CHEMISTRY
February, 1927
of pressure which would oppose the general fall of pressure produced by the main course of the reaction. It appears to be generally conceded a t presentlo that ionization does not play a primary role in explosive reaction or flame propagation. It has been shown here that in the ionized oxidation of methane the presence of an antiknock does not retard but rather accelerates the reaction, probably by taking part in it through enhancing the absorption of the energy of alpha-radiation, May we assume that the function of the antiknock in ordinary combustion is a similar one under the influence of some other type of radiation, possibly infra-red? This was the original theory entertained by Midgley, though he was employing it to explain retardation rather than acceleration. Symposium of the Faraday Society on "Explosive Reactions in Gaseous Media," London, June, 1926. 10
233
The writers are not aware that any direct evidence exists that the antiknock does actually reduce the velocity of flame propagation. The idea has been recently expressed" that it does the opposite, by facilitating and in making the initiation of flame more instantaneous and uniform. This would appear to be more in accord with the present results as far as they are comparable, and also with a suggestion of one of the writerP that non-selective absorption dependent on the absolute density of the gas mixture may be an important factor in flame propagation just as it is in the reaction proceeding under the influence of alpha-radiation. 1 1 Charch, Mack, and W o o d , THISJOURNAL, 18, 338 (1926); also H. S. Taylor, private communication. 12 Lind, J. Chem. Sac. (London), 126, 1867 (1924).
Some Chemical Characteristics of Sewage Sludge' By S. L. Neave with A. M. Buswell STATE WATER SURVEY
DIVISION, U R B A N A , ILL.
T
HE bacterial digestion of sewage sludge under anaerobic conditions has received considerable attention in recent years, partly because it is a necessary step in the production of an inoffensive, rapidly drying product, and partly on account of the economic value of the combustible gases evolved during the process. Very little is known of the chemistry or the bacteriology involved, though the interesting work of Rudolfs2 in this country and of Imh~ffB , ~a ~ h S, ~i e r ~ and , ~ Groenewege6 on the Continent has already shown something of the complexity of the problem. From the viewpoint of the plant operator we need first a simple method of determining wheri a given sludge is "ripe," or sufficiently digested to be run onto the drying bed. Rudolfs has recently shown a relation between the biochemical oxygen demand of the sludge and its course of digestion. At the experimental plant of the Illinois State Water Survey Division, the writers have been following the volatile-matter content of dry sludge as a similar index. The ratio of volatile matter to fixed carbon is known to decrease in passing from wood through peat to coal (Table I). Table I'I
FIXEI)
VOLATILE MATTER ~
Wood Peat Lignite Anthracite a
Per cent 7 5 to 79 i o . 06 60.67 6.18
CARBON ~~~
~
Per cent 21 to 25 29.94 39.33 93.8%
Parr, Illinois Geol. Suruey, Bull. 3.
Consideration of the data in Table I suggested the probability that raw sludge would contain more volatile matter and less fixed carbon than digested sludge. If this were true and the variation proved to be sufficiently wide and consistent, the determination of volatile matter and fixed Presented before the Division of Water Sewage and Sanitation at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. * New Jersey Agr. Expt. Sta., Bull. 427 (1925). * Eng. News-Record, 91, 512 (1923); 93, 585 (1924). 4 Bach and Sierp, Cent?. Bakt. Parasitenk., I I A b f . , 69, 1 (1923); 60, 318 (1923). 6 Tech. Getneindebl., 27, 213 (1924); Gas Wasserfach, 68, 773 (1925). 6 Mededeel. Geneeskund. Lab. Wetlevreden, 1920, 163. 1
'
VOLATILEMATTER
hf A T E R I A L
Freshsolids Direstedsludge
SLUDGE A5 SAXPLED
FIXED
ASH-FREE BASIS
Max
Min.
Av.
Max
Min
Av.
%
c/o
R
70
%
70
70.9 61.2
46.5 4.5 9
59 3 97 0 8 3 . 9 9 0 . 8 54.9 92.7 86.2 89.5
Max. Min. Av.
70% 9.6 2.2 8.8 3.8
% 5.5 6.4
The use of the volatile and fixed carbon determination to distinguish between fresh and digested sludge does not appear to be feasible. It is a useful test in a research study of the character of sludge and there is still a possibility that the data so obtained may be correlated with the ripeness of the sludge. 7 Parr, "The Analysis of Fuel, Gas, Water, and Lubricants," p. 146, (1922). 8 Rather, THISJ O U R N A L , 10, 439 (1918).
